The present invention relates to a surveying instrument enabling to confirm a collimating point and a target by emitting a visible point light and by confirming a projecting position of the point light.
When surveying operation is carried out at a building site or a construction site, a surveying instrument provided with a visible laser projecting device is often used to confirm a collimating point of the surveying instrument or to identify a target for surveying.
In the surveying instrument, a visible laser beam projected from the visible laser projecting device fulfills a function of a point light to indicate a point to be measured for an operator at the surveying target. The operator performs operation such as marking of a measuring point at the position indicated by the visible laser beam.
In particular, when operation is to be performed in dark conditions such as in a tunnel, a measuring position can be clearly defined by projecting a point light. For instance, excavating operation is carried out according to a projecting point of the point light.
FIG. 4 is a block diagram showing a surveying instrument provided with a visible laser projecting device.
It is designed in such a structure that the visible laser beam is projected along a collimation axis of a telescope as a light to be projected to a collimation point. A semiconductor laser is now used instead of a conventional gas laser type light source, and the visible laser projecting device and the visible laser beam can be incorporated in the surveying instrument.
First, description will be given on a collimation optical system 1.
The collimation optical system 1 comprises a collimation optical axis 2. On the collimation optical axis 2, there are provided an objective lens 3, a focusing lens 4, an erect image prism 5, a focal plate 6, and an ocular lens 7. By moving the focusing lens 4 along the collimation optical axis 2, an image of a collimation point is formed on the focal plate 6 under focused condition.
A polarization beam splitter 8 is provided between the focusing lens 4 and the erect image prism 5. The polarization beam splitter 8 has a polarizing reflection surface 8a. The polarizing reflection surface 8a reflects a s-polarized light and allows a p-polarized light to pass, for instance.
Next, a visible laser projecting device 9 has a projection optical axis 10. The projection optical axis 10 crosses the collimation optical axis 2 within the plane of the polarizing reflection surface 8a and commonly shares (with the collimation optical axis 2) a portion closer to the collimation target from the polarization beam splitter 8.
On the visible laser projecting device 9, there is provided a semiconductor laser 11, which serves as a light source to emit the visible laser beam. A condenser lens 12 is disposed between the semiconductor laser 11 and the polarization beam splitter 8. In this case, the output from the semiconductor laser 11 is limited to about several milliwatts because the laser beam has directivity and high energy density.
In the surveying instrument as described above, a collimation light from a target for surveying forms an image on the focal plate by the objective lens 3 and the focusing lens 4, and the surveying operator can see the image of the target for surveying on the focal plate 6 via the ocular lens 7.
The point light from the visible laser projecting device 9 is a s-polarized light. It is reflected by the polarizing reflection surface 8a and is projected to the target for surveying through the focusing lens 4 and the objective lens 3.
The visible laser beam reflected by the target for surveying passes through the objective lens 3 and the focusing lens 4 and reaches the polarizing reflection surface 8a. When the visible laser beam is reflected by the target for surveying, uniformity of the polarization is disrupted, and the reflected visible laser beam contains a p-polarized component. Therefore, the p-polarized component of the reflected visible laser beam passes through the polarizing reflection surface 8a. The surveying operator can recognize the reflected visible laser beam and can confirm the projecting position of the visible laser beam on the target for surveying.
A surveying instrument with the above arrangement is described, for instance, in JP-A-10-132557.
When the target for surveying is made of a retroreflection prism or there is an object such as glass with high reflectivity in the measuring direction, and if the visible laser beam is reflected by the retroreflection prism or the glass, etc., the surveying operator must directly see the strong visible laser beam converged via the collimation optical system 1.
As described above, the output of the visible laser beam is low in itself, but the laser beam has directivity and high energy density. When the surveying operator directly sees the visible laser beam, he may feel dizziness. Also, after directly seeing the visible laser beam, the operator is often turned to a condition not suitable for adequate operation because of an afterimage remaining for some time.
There is another type of surveying instrument, in which a distance is measured by a visible light instead of a visible laser beam. In such type of surveying instrument, the operator often directly sees a distance-measuring light reflected by a prism. In such case, the surveying operator often feels dizziness in the same matter, or is turned to a condition not suitable for operation because of an afterimage.
In the conventional type surveying instrument as described above, a visible laser projecting device is used to illuminate a point to be measured. In case the visible laser projecting device emits a point light to indicate a measuring point, light density is increased. When the surveying operator directly sees the reflected point light, he may feel much higher dizziness.